When Eve's boss asks her to fetch him a cup of tea, she manages to smile sweetly. "I make him tea because it's my job. But tea-making doesn't require a degree in French and linguistics."

Eve's degree comes from Oxford, but the 29-year-old has been working as a PA for the past five years. "I work mostly for people who have fewer academic qualifications than me and much of what I do is menial. But I have an active life outside of work - I'm very involved in amateur dramatics - and I get very annoyed if I have a job that means I can't attend rehearsals.

"I once had a job in banking, which was great until 18 months down the line I quit because I was so exhausted. I managed to fit in only one play in that time and even then I couldn't remember my lines because I was so tired. Now I work just to pay the bills."

She is not alone. There are many well-qualified, intelligent people who spend their 9 to 5 working in clerical posts, sales, bars, call centres or restaurants. But some, such as Eve, choose not to moan about their dull, menial or repetitive work because they simply don't see the attraction of a prestigious, high-paying career. They - let's call them the "happily underemployed" - reject the idea that their work is their "calling". They work only to live.

When it comes to underemployment, Britain is a world leader. UK workers are some of the least engaged and emotionally attached to their companies in the world. A survey of 15,000 workers by research firm ISR reckons a third of all workers are indifferent to their work and employer. It's not just a British condition, though. A quarter of Americans show up at work "just for the pay cheque", says research group TNS.

But the happily underemployed are not slackers. They go about their work honestly and professionally. They don't "goof off" on company time. "Conducting market research interviews is like a factory job," admits Michael, a 29-year-old English graduate from a top university, who previously worked in paralegal and teaching jobs. "But I have a gene that takes satisfaction from being able to point to a physical product I've made. Feeling like a cog in a machine is not necessarily a bad thing. I don't have existential crises at my desk."

Being happily underemployed runs counter to the prevailing wisdom that passion should be as common in the workplace as in the bedroom. These people are passionate - just not about their work. They reserve their passion for pursuits outside of work, whether it's amateur dramatics, playing in a band, film-making, painting or rock-climbing. So long as they earn just enough to service their debts and finance their hobbies, the happily underemployed are willing to forgo working a "fulfilling" 80-hour week for fun, satisfying lives outside the office.

"The happily underemployed are actually often fully employed - but not in the course of their paid work," says Adrian Furnham, professor of psychology at University College, London. "They're often very busy with hobbies and passions that are intrinsically motivating."

These people are dropping out of the rat race - except they're doing it at work. They don't feel compelled to imprison the meaning of life in their careers. "An outside interest give structure and meaning to their lives," explains Furnham. "It gives them a friendship and social support network and a sense of identity too."

Of course, few people leave university plotting a career in underwhelming jobs. But student debt and "degree glut" have precipitated a shift from graduate unemployment to underemployment. In the early 1960s, the percentage of young people going to university was 5%. Today that figure is closer to 45%. And since the number of "graduate jobs" has failed to keep pace, up to 45% of graduates from some disciplines are destined for menial work, says the National Institute of Economic and Social Research.

Saddled with debts of, on average, £13,000, an increasing number of graduates relegate chasing their perfect job behind getting themselves back into the black. But escaping "transitory" non-graduate roles can be as easy as climbing out of quicksand. Seven years after leaving university, one in 10 are still in "non-graduate" jobs, according to the universities of Warwick and the West of England.

But the happily underemployed are, in fact, exercising choice. "I chose in my mid-20s to buy a house, when I had a job with a dotcom," explains Eve. "It's my choice to keep that mortgage rather than sell up and pursue a career change. I don't deny that I'd like to have a job I love, but to work in theatre I'd have to take a 50% pay cut."

A decade ago, in a tract for thinktank Demos, David Cannon described what he saw as a different work ethic among Generation X - those born between 1965 and 1978. A decline in loyalty to employers meant young workers saw work in purely transactional terms. What's the deal? What's in it for me? Why get saddled with a stressful job?

The happily underemployed are less likely to channel their passions into a job. The purpose of the working week is to get them to the weekend, when the fun begins. While their friends in investment banking or law will spend much of today flaked out in front of a TV, Eve and Michael are ready for action.

Where the office zombies roam

There's another group of workers not so happy in their underemployment. Like the happily underemployed, their abilities are completely wasted. But these people have no outlet for their passion. No outside interests. They're not being fulfilled in any area of their lives.

David Bolchover, author of new book The Living Dead (Capstone), reckons he did no more than six months' work in six years working for a City insurance firm. The implications, he says, are grave.

"Being bored at work inevitably affects your relationships, energy levels outside of work and self esteem. Not much good can come from doing nothing for long periods of time."